Multicarrier transmitting apparatus

ABSTRACT

A multicarrier transmitting apparatus capable of providing a fast cell search. A base station apparatus ( 100 ), which serves as a multicarrier transmitting apparatus for transmitting frames each including, as synchronization channel sequences, first synchronization sequences (P-SCH sequence) used for timing determinations and second synchronization sequences (S-SCH sequence) different from the first synchronization sequences, comprises a frame forming part ( 130 ) that forms frames each including the first synchronization sequence (P-SCH sequence) disposed in each of subcarriers symmetrical with respect to a DC component subcarrier (DC subcarrier) in the frequency direction; and an RF transmitting part ( 160 ) that transmits the frames. In this way, a frame receiving end can use a filter having a polarly symmetrical pass-band and needs no frequency shifting process, with the result that the processing amount at the receiving end can be reduced and hence a fast cell search can be achieved.

TECHNICAL FIELD

The present invention relates to a multicarrier transmitting apparatus. More particularly, the present invention relates to a multicarrier transmitting apparatus for transmitting a frame including synchronization channels used in establishing synchronization at the receiving side.

BACKGROUND ART

In the standards organization 3GPP, studies are conducted for 3GPP RAN LTE (Long Term Evolution) to realize further improvement of present third mobile phone systems.

Presently in LTE standardization meetings, a synchronization channel (SCH) transmission method for detecting synchronization of an OFDM (Orthogonal Frequency Division Multiplexing) signal is discussed, and various methods are proposed for multiplexing a primary SCH (P-SCH) and a secondary SCH (S-SCH).

Non-Patent document 1 discloses one of P-SCH and S-SCH multiplexing method examples. The document discloses a P-SCH and S-SCH frequency division multiplexing method, in which P-SCHs are multiplexed subcarriers having lower frequencies and S-SCHs are multiplexed on subcarriers having higher frequencies, with respect to a DC subcarrier (see FIG. 1). To perform timing synchronization processing using a replica-based correlation method at the receiving side of the frame formed in this multiplexing method, only the P-SCH is extracted by a bandpass filter (BPF) and subjected to correlation calculation with a P-SCH replica, and symbol timing, subframe timing, and so on are detected from the timing a peak occurs.

Non-patent Document 1: NTT DoCoMo, et al, “SCH Structure and Cell Search Method for E-UTRA Downlink,” 3GPP TSG RAN WG1 Meeting *44 R1-060311 DISCLOSURE OF INVENTION Problems To Be Solved By the Invention

As described above, to perform timing synchronization processing using a replica-based correlation method, it is necessary to extract the P-SCH, and, in the cases of P-SCH and S-SCH multiplexing methods (see FIG. 1) such as conventional techniques, the following two P-SCH extracting methods are possible.

The first method is to make a received signal pass a BPF having an asymmetrical passband as shown in FIG. 2. The second method is to make a received signal pass a lowpass filter (LPF) after frequency shift, as shown in FIG. 3.

However, in the above-described first method, a filter coefficient of a BPF become complex numbers, and so the amount of filter processing is twice as much as filter processing using real numbers, and therefore the amount of processing at the receiving side increases. Further, in the above-described second method, filter processing is performed after the P-SCH is placed in the center, so that the filter coefficient becomes real numbers. Nevertheless, frequency shift processing is required, and, multiplication processing for the frequency shift is required, and therefore the amount of processing at the receiving side increases. That is, any methods make the amount of processing increase at the receiving side, and therefore the time for cell search takes longer.

It is therefore an object of the present invention to provide a multicarrier transmitting apparatus realizing high speed cell search.

Means for Solving the Problem

The multicarrier transmitting apparatus of the present invention provides transmitting a frame in which a first synchronized sequence used in detecting a timing and a second synchronized sequence different from the first synchronized sequence as a synchronization channel sequence and adopts a configuration including: a frame forming section that forms a frame in which a first synchronized sequence is allocated to a subcarrier symmetrically with respect to a subcarrier of a direct-current component in the frequency domain; and a transmitting section that transmits the frame.

Advantageous Effect of the Invention

According to the present invention, it is possible to provide a multicarrier transmitting apparatus realizing high speed cell search.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 explains a conventional synchronization channel allocation method;

FIG. 2 explains one possible example of a method of filtering at the receiving side a frame in which synchronization channels are allocated using the method in FIG. 1;

FIG. 3 explains another possible example of a method of filtering at the receiving side a frame in which synchronization channels are allocated using the method in FIG. 1;

FIG. 4 is a block diagram showing the configuration of the multicarrier communication system according to the Embodiment of the present invention;

FIG. 5 is a frame configuration of the multicarrier communication system in FIG. 4 and explains the operations of the multicarrier communication system; and

FIG. 6 is another frame configuration of the multicarrier communication system in FIG. 4 and explains the operations of the multicarrier communication system.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 4, the multicarrier communication system of the present embodiment has base station apparatus 100 as a multicarrier transmitting apparatus and mobile terminal apparatus 200 as a multicarrier receiving apparatus.

Base station apparatus 100 has P-SCH generating section 110, S-SCH generating section 120, frame forming section 130, inverse fast Fourier transform (IFFT) section 140, CP (Cyclic Prefix) inserting section 150 and RF transmitting section 160.

P-SCH generating section 110 generates a P-SCH sequence used to detect timing such as symbol timing and frame timing at the receiving side.

S-SCH generating section 120 generates a S-SCH sequence used to specify the scrambling code group in which the base station scrambling code of the base station apparatus is included (i.e. base-station specific code) at the receiving side.

Frame forming section 130 inputs the P-SCH sequences from P-SCH generating section 110, the S-SCH sequences from S-SCH generating section 120 and transmission data (not shown) such as data channels transmitted in the channels other than synchronized sequences, to form a frame using the input signals. Frame forming section 130 forms a frame having the configuration shown in the left of FIG. 5. That is, frame forming section 130 forms a frame by allocating the P-SCH sequences symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain, and by allocating the S-SCH sequences to both outer sides of the P-SCH sequences in the frequency domain,

To be more specific, frame forming section 130 has subcarrier mapping section 132 and frame configuring section 134.

Subcarrier mapping section 132 inputs the P-SCH sequences from P-SCH generating section 110 and the S-SCH sequences from S-SCH generating section 120 and maps the P-SCH sequences to the subcarriers, which are symmetrically with respect to the DC subcarrier in the frequency domain and which are continuous in the frequency domain, among the subcarriers prepared in the base station apparatus. Further, subcarrier mapping section 132 maps the S-SCH sequences to the subcarriers to both outer sides of the subcarriers where the P-SCH sequences are allocated in the frequency domain.

Frame configuring section 134 forms a frame by allocating other channels including transmission data to symbols other than the symbols where the P-SCHs and the S-SCHs are allocated, to form a frame, and outputs the frame to IFFT section 140.

Inverse fast Fourier transform (IFFT) section 140 performs an IFFT on the frame formed in frame forming section 130, to form an OFDM signal, and outputs the OFDM signal to CP inserting section 150.

CP inserting section 150 inserts a CP (cyclic prefix) in the OFDM signal from IFFT section 140, and outputs the OFDM signal to RF transmitting section 160.

RF transmitting section 160 performs radio transmitting processing (e.g. digital-to-analog conversion processing and up-conversion processing to radio frequency bands) on the OFDM signal where a CP is inserted in CP inserting section 160, and transmits the OFDM signal via the antenna.

Further, mobile terminal apparatus 200 has RF receiving section 210, filter processing section 220, replica correlation processing section 230, and timing detection processing section 240.

RF receiving section 210 performs radio receiving processing (e.g. down-conversion processing to a baseband bandwidth and analog-to-digital conversion) on a received signal received via the antenna, and outputs the received signal after radio receiving processing to filter processing section 220.

Filter processing section 220 receives as input the signal after radio receiving processing from RF receiving section 210, extracts only the signal of the passband, and outputs the extracted signal to replica correlation processing section 230. In the present embodiment, as described above, the frame where the P-SCH sequences are allocated symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain and the S-SCH sequences are allocated to both outer sides of the P-SCH sequences in the frequency domain, is received, so that filter processing section 220 is set up such that only the bandwidth where the P-SCH sequences are allocated passes.

Replica correlation processing section 230 performs correlation calculation between the signal from filter processing section 220 and a P-SCH sequence replica, and outputs the correlation result to timing detection processing section 240.

Timing detection processing section 240 detects a peak in the correlation result from replica correlation processing section 230, and detects symbol timing, subframe timing and so on, from the timing the peak occurs. Based on the timing detected in timing detection processing section 240, in the succeeding processing sections, the S-SCH sequence included in the signal after radio receiving processing is extracted, and, from the S-SCH sequence, the code group is identified and the scrambling code is further identified. As such, a series of cell search processing is completed.

Next, the operations of the multicarrier communication system having the above configuration will be explained with reference to FIG. 5.

As shown in the left of FIG. 5, frame forming section 130 of base station apparatus 100 forms a frame where the P-SCH sequences are allocated symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain and the S-SCH sequences are allocated to both outer sides of the P-SCH sequences in the frequency domain. This frame is subjected to predetermined processing in IFFT section 140, CP inserting section 150 and RF transmitting section 160 and transmitted via the antenna.

In mobile terminal apparatus 200 of the receiving side, the signal transmitted from base station apparatus 100 is received via the antenna, subjected to predetermined processing in RF receiving section 210 and then inputted in filter processing section 220.

In filter processing section 220, only the signal of frequency band in which a zero frequency is placed in the center and the P-SCH sequences are allocated in base station apparatus 100 of the transmitting side passes. At this time, the frame where the P-SCH sequences are allocated symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain is transmitted from base station apparatus 100 of the transmitting side, so that, in mobile terminal apparatus 200 of the receiving side, filter processing section 220 having a symmetrical passband (see the center of FIG. 5) can be used. That is, the filter coefficient becomes only real numbers. Further, conventional frequency shift processing is not required. Consequently, by transmitting from base station apparatus 100 the frame where the P-SCH sequences are allocated symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain, the amount of processing at the receiving side is reduced, and cell search can be made high speed.

In replica correlation processing section 230, correlation calculation is carried out between the signal passing filter processing section 220 and a P-SCH sequence replica (see the right of FIG. 5).

A case has been explained with the above description where base station apparatus 100 of the transmitting side transmits the frame in which the P-SCH sequences are allocated to the subcarriers symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain and continuous in the frequency domain, among the subcarriers prepared in the base station apparatus. However, the present invention is not limited to this, and, as shown in the left of FIG. 6, the subcarriers where the P-SCHs are allocated are placed symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain and may be made spaced apart frequency-wise with respect to the DC subcarrier. That is, the frame where the P-SCH sequences are allocated symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain may be transmitted from base station apparatus 100 of the transmitting side.

Incidentally, when the subcarriers where the P-SCH sequences are allocated are placed symmetrically with respect to the DC subcarrier (i.e. direct-current components) in the frequency domain and made spaced apart frequency-wise with respect to the DC subcarrier, as shown in the center of FIG. 6, filter processing section 220 has a non-passband in which a zero frequency is placed in the center and has passband to both sides of the non-passband. Then, correlation calculation is carried out between the signal of the bandwidth passing through filter processing section 220 and the P-SCH sequence replica (see the right of FIG. 6).

In this way, according to the present embodiment, base station apparatus 100 as a multicarrier transmitting apparatus for transmitting a frame in which first synchronized sequences (i.e. P-SCH sequences) used in detecting timings and second synchronized sequences (i.e. S-SCH sequences) different from the first synchronized sequences as synchronization channel sequences, has: frame forming section 130 forming a frame in which the first synchronized sequences (i.e. P-SCH sequences) are allocated to the subcarriers symmetrically with respect to the subcarrier of direct-current components (i.e. DC subcarrier) in the frequency domain, and RF transmitting section 160 transmitting the frame.

By this means, the amount of processing can be reduced at the frame receiving side, and cell search is performed at high speed as described above.

INDUSTRIAL APPLICABILITY

The multicarrier transmitting apparatus of the present invention is suitable for use in realizing high speed cell search at the receiving side. 

1. A multicarrier transmitting apparatus for transmitting a frame in which a first synchronized sequence used in detecting a timing and a second synchronized sequence different from the first synchronized sequence as a synchronization channel sequence, the multicarrier transmitting apparatus comprising: a frame forming section that forms a frame in which a first synchronized sequence is allocated to subcarriers symmetrically with respect to a subcarrier of a direct-current component in the frequency domain; and a transmitting section that transmits the frame.
 2. The multicarrier transmitting apparatus according to claim 1, wherein the frame forming section allocates a second synchronized sequence to a subcarrier different from the subcarrier to which the first synchronized sequence is allocated. 